Auditory adaptation and masking of evoked potentials have striking developmental effects. The magnitude of these phenomena increases with decreasing age. Basic knowledge concerning developmental adaptation effects (the effect of a series of stimuli on the response to any stimulus in the series) is lacking. It seems likely that there are developmental differences in 1) the time necessary to reach the adapted state; 2) the time necessary to recover from the adapted state; 3) the range of repetition rates which affect the evoked response; 4) frequency specific adaptation; and 5) central and peripheral adaptation effects. Few data exist concerning developmental differences in auditory masking of evoked potentials. The details of developmental differences in simultaneous (the masker and signal occurring at the same time), forward (the masker preceding the signal), and backward (the masker following the signal) are unknown. This proposal investigates in human newborns and adults auditory adaptation and masking of surface recorded brainstem and cortical evoked potentials.